Fix bug that crashed a master is a slave attempted to re-register with more than one task running in the same executor.
Fix bug that crashed a master is a slave attempted to re-register with more than one task running in the same executor.

git-svn-id: 03d7800a49d8905ef4fbcc296184319e19243493@1241991 13f79535-47bb-0310-9956-ffa450edef68

dforsyth/mesos,abudnik/mesos,zmalik/mesos,neilconway/mesos,verizonlabs/mesos,wickman/mesos,jpeach/mesos,reneploetz/mesos,reneploetz/mesos,asamerh4/mesos,Aman-Jain-14/customizedMesos,Gilbert88/mesos,verizonlabs/mesos,abudnik/mesos,yuquanshan/customizedMesos,jpeach/mesos,abudnik/mesos,verizonlabs/mesos,asamerh4/mesos,chhsia0/mesos,chhsia0/mesos,zmalik/mesos,kaysoky/mesos,andschwa/mesos,Aman-Jain-14/customizedMesos,neilconway/mesos,gsantovena/mesos,kaysoky/mesos,wickman/mesos,dforsyth/mesos,neilconway/mesos,gsantovena/mesos,kaysoky/mesos,reneploetz/mesos,jpeach/mesos,yuquanshan/customizedMesos,andschwa/mesos,yuquanshan/customizedMesos,Aman-Jain-14/customizedMesos,enachb/mesos,jpeach/mesos,Gilbert88/mesos,asamerh4/mesos,wickman/mesos,gsantovena/mesos,kaysoky/mesos,craimbert/mesos,chhsia0/mesos,craimbert/mesos,yuquanshan/customizedMesos,zmalik/mesos,yuquanshan/customizedMesos,chhsia0/mesos,craimbert/mesos,neilconway/mesos,yuquanshan/customizedMesos,kaysoky/mesos,zmalik/mesos,asamerh4/mesos,Gilbert88/mesos,wickman/mesos,asamerh4/mesos,zmalik/mesos,samwhitlock/mesos-monitoring,wickman/mesos,reneploetz/mesos,reneploetz/mesos,gsantovena/mesos,enachb/mesos,reneploetz/mesos,reneploetz/mesos,gsantovena/mesos,jpeach/mesos,Gilbert88/mesos,abudnik/mesos,dforsyth/mesos,jpeach/mesos,samwhitlock/mesos-monitoring,jpeach/mesos,craimbert/mesos,enachb/mesos,verizonlabs/mesos,samwhitlock/mesos-monitoring,samwhitlock/mesos-monitoring,verizonlabs/mesos,asamerh4/mesos,samwhitlock/mesos-monitoring,andschwa/mesos,neilconway/mesos,dforsyth/mesos,yuquanshan/customizedMesos,wickman/mesos,Aman-Jain-14/customizedMesos,Gilbert88/mesos,abudnik/mesos,asamerh4/mesos,Aman-Jain-14/customizedMesos,craimbert/mesos,kaysoky/mesos,gsantovena/mesos,verizonlabs/mesos,dforsyth/mesos,samwhitlock/mesos-monitoring,neilconway/mesos,wickman/mesos,craimbert/mesos,chhsia0/mesos,dforsyth/mesos,Gilbert88/mesos,andschwa/mesos,enachb/mesos,enachb/mesos,andschwa/mesos,enachb/mesos,abudnik/mesos,zmalik/mesos,abudnik/mesos,dforsyth/mesos,craimbert/mesos,Aman-Jain-14/customizedMesos,enachb/mesos,Gilbert88/mesos,andschwa/mesos,andschwa/mesos,neilconway/mesos,zmalik/mesos,gsantovena/mesos,kaysoky/mesos,verizonlabs/mesos,Aman-Jain-14/customizedMesos,chhsia0/mesos,chhsia0/mesos